1. Field of the Invention
The present invention relates to washing machines and more particularly to moving clothes within the wash chamber of an automatic washer.
2. Description of the Related Art
Known washing machines include agitator washing machines and impeller washing machines. Agitator washing machines use a water bath, in conjunction with clockwise and counter-clockwise agitator oscillations, to promote mechanical action inside a wash basket. In general, these machines tend to move a clothes load down through the center of the wash basket, generally parallel to the centerline of the agitator, then radially outward along the wash basket bottom, then upward and generally parallel to the sides of the wash basket, and then inward across the top of the water bath.
Impeller washing machines generally move the clothes in a rotating vortex-like motion that is centered about the impeller axis. This vortex washing motion often results in the tangling of clothes into rope-like masses. Tangled clothes do not wash well, may transfer dyes between clothes, and may have more wrinkles than untangled clothes when dried.
In typical washing machines, both impeller and agitator oscillations are symmetric and constant during the majority of a wash cycle. FIG. 1 depicts a typical symmetrical agitator or impeller oscillation period during a typical wash cycle. In FIG. 1, signals above the horizontal time axis indicate a clockwise rotation signal, signals along the time axis indicate no rotation signal (motor off) or a pause, and signals below the time axis indicate a counter-clockwise rotation signal. The illustrated oscillation period includes a 0.5 second clockwise (motor on) time, followed by a 0.5 second pause (motor off), followed by a reversing 0.5 second counter-clockwise (motor on) time, followed by a 0.5 second pause (motor off). The oscillations are constant, in that the period is then repeated, as illustrated in FIG. 1. In some agitator washing machines, the oscillations are achieved with a fixed-speed motor and a mechanical, reversing transmission. Other agitator washing machines use a reversing motor and electronic switching controls.
The oscillation patterns can also be more complex. This complexity can take several forms. One form observed in typical impeller machines is that longer oscillation periods are used, e.g., 8 seconds clockwise (motor on), 8 seconds pause (motor off), 8 seconds counter-clockwise (motor on), 8 seconds pause (motor off). Another typical form of complexity is that, within an oscillation period, non-symmetric motor profiles can be used, e.g., 8 seconds clockwise (motor on), 2 seconds pause (motor off), 8 seconds counterclockwise (motor on), 2 seconds pause (motor off). The relatively higher value of motor on times in both of these typical patterns results in the disadvantage of severe clothes tangling. These higher motor on time values, however, are common to the washing machine industry.
One additional known form of complexity is observed in agitator washers. Some washer models change to an increased-time period for the symmetric oscillations near the end of the wash cycle. For example, a washer may have a 0.5-second on/pause/on/pause oscillation pattern for 11 minutes of washing, then change to a 0.8 second on/pause/on/pause oscillation pattern for the last minute of the wash cycle. This change is performed in an attempt to reduce tangling of the clothes load and to distribute the clothes load evenly in the basket prior to spin and water extraction. The evenly distributed clothes have a reduced tendency to cause an off-balance condition during the spin. In some agitator washers, however, this change in the cycle requires the use of a multi-speed motor and a reversing transmission. The higher cost of the multi-speed motor represents a disadvantage.
Engineering efforts to reduce water usage in impeller machines resulted in the discovery of the inverse toroidal motion (LaBelle, et al., U.S. Pat. No. 6,520,396). An inverse toroidal motion washing machine uses an impeller plate with a reduced water amount. The clothes load in this washing machine moves radially inward across the impeller plate, up through the center of the wash basket, then radially outward along the top of the water bath, then downward and generally parallel to the sides of the wash basket. This clothes motion, or rollover, typically occurs with an approximately 0.5-second symmetric and constant impeller oscillation pattern, as depicted in FIG. 1. With this clothes motion and oscillation pattern, however, two problems exist.
First, when using symmetrical impeller oscillations, larger wash loads tend to be less inclined to begin the inverse toroidal roll and are more “lethargic” in their motion than smaller clothes loads. Reduced rollover is often associated with poor wash performance on soils like carbon that require mechanical action. Second, when using symmetrical impeller oscillations with small to medium-sized loads, the uniformity of the load within the wash basket is not assured. This non-uniformity can lead to an off-balance condition during basket spin.
The non-uniformity of the load problem is specifically observed in low-water impeller machines, and appears to be related to higher oscillation cycle times. This problem has been called “bunch and slosh.” “Bunch and slosh” is a term used by one of skill in the art to describe clothes load distribution about the wash basket diameter during low-water levels. At certain times during the wash cycle, a majority of the clothes load can be observed from the top of the washer as being gathered into one quadrant of the wash basket (i.e., a “bunch”), leaving a minority of the load in the remaining quadrants. The quadrants with the minority of the clothes have a higher water-to-clothes ratio, and often these areas contain only water (i.e., they create a “slosh” sound). This non-uniform configuration inside the wash basket is undesirable for several reasons. First, it can result in an off-balance situation during wash basket spin, if the non-uniformity exists at the end of the wash cycle. Second, the tightly packed “bunch” of clothes does not expose the center of the “bunch” to the mechanical action of cloth-to-cloth motion and the mechanical action of cloth-to-impeller motion. This lack of mechanical action, which is needed to remove certain soils from the clothes, can limit the performance of low-water impeller machines. Third, it has been observed that the typical inverse toroidal motion tangles clothes loads less than does the action of a deep-water impeller wash, however, this reduced-tangle advantage is not achieved when the “bunching” of the load occurs. This is because the load movements that create “bunching” (i.e., move the clothes load to a concentrated mass in the basket) are different than the load movements that give rise to inverse toroidal roll (i.e., move the load radially and uniformly inward). In summary, “bunching” appears to preclude uniform inverse toroidal rolling.
Based on the above-described problems of washing machines, it is therefore desirable to improve them.